The subject matter disclosed herein relates to turbines and, more particularly, to systems for controlling the thermal condition of a steam turbine rotor support, specifically a rotor bearing support.
Some power plant systems, for example certain nuclear, simple cycle and combined cycle power plant systems, employ turbines in their design and operation. Some of these turbines include rotating portions (e.g., rotors) which are supported by rotor bearing supports within the turbine. These rotor bearing supports stabilize a position of the rotors and enable the rotors to be rotatable within the turbine. During operation, a working fluid (e.g., high temperature steam, high temperature gas, etc.) is directed through the turbine and across a length of the rotor; this working fluid driving the rotor to produce power for a variety of applications. Some of these rotors may have a substantial length which requires the use of multiple rotor bearing supports within the turbine. The location and proximity of the rotor bearing supports to the rotor may result in exposure to substantial thermal gradients. With differences in these thermal gradients ranging in the hundreds to thousands of degrees Celsius, the rotor bearing supports may significantly expand and contract in response to the temperature variations which occur during operation of the turbine. These expansions and contractions may adjust a height of the rotor bearing supports and subsequently a position of the rotor, requiring the turbine to include increased radial clearances between the rotor and turbine which may decrease system efficiency. Further, in turbines with lengthy rotors requiring multiple rotor bearing supports, variations in thermal conditions throughout the rotor may cause differential thermal variations between each of the rotor bearing supports, resulting in misalignment of the rotor.
Referring to FIG. 1, a schematic view of portions of a turbine 100 is shown with a rotor 104 supported within a portion of a casing 130 by first rotor bearing support 120 and second rotor bearing support 122. Turbine 100 illustrated in FIG. 1 is a known turbine which is shown during operation exposed to a thermal gradient TG. Thermal gradient TG represents varying thermal conditions within turbine 100 which decrease incrementally in temperature from first rotor bearing support 120 toward rotor bearing support 122, with respect to the axial position. As shown in FIG. 1, thermal gradient TG is greater at first rotor bearing support 120 which is positioned axially downstream of rotor bearing support 122. As can be seen, casing 130, which is supported by a casing support 133 has an aligned/linear shape. In contrast, rotor bearing supports 120 and 122 have expanded as a result of exposure to thermal gradient TG, and these expansions have caused rotor 104 to partially deform in a non-linear manner. Furthermore, as a result of temperature variations across thermal gradient TG, rotor bearing support 120 has expanded to a greater height than rotor bearing support 122 resulting in a further misalignment of rotor 104.